Cube Steaks

Name: Cube Steaks
Prep time: 20 min
Cook time: 3 h
Total time: 3 h 20 min
Cuisine: American
Ingredients: 2 pounds cube steaks; ⅓ cup all purpose flour; ½ teaspoon kosher salt; ¼ teaspoon black pepper; 1 tablespoon olive oil; 2 tablespoons butter; 2 large yellow onions (sliced into ¼" rings); ½ cup red wine (or beef broth); 3-4 cups beef broth (+ 1 cup, not low sodium); 2 tablespoons balsamic vinegar; 1 teaspoon Dijon mustard; 2 sprigs fresh rosemary (or ½ teaspoon dried crushed rosemary); 1 tablespoon cornstarch (or as needed)